1 Technical Field
The present invention relates to semiconductor modules that have semiconductor elements built therein and electric power conversion apparatuses that employ the semiconductor modules.
2 Description of Related Art
There are known semiconductor modules that are employed in electric power conversion apparatuses (see, for example, Japanese Patent Application Publication No. JP2014229642A). The semiconductor modules have, for example, an IGBT (Insulated-Gate Bipolar Transistor) built therein; the IGBT is made of a silicon semiconductor. The electric power conversion apparatuses are configured to perform electric power conversion by controlling switching of the IGBT.
In recent years, there has been growing demand for low-loss semiconductor modules. In an attempt to meet this demand, a semiconductor module has been investigated where an IGBT made of a silicon semiconductor and a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) made of a wide-bandgap semiconductor (e.g., SiC or GaN) are connected in parallel to each other. The IGBT has, due to the existence of a diffusion potential therein, a high on-resistance in a relatively low-current region. In contrast, the MOSFET made of the wide-bandgap semiconductor has a low on-resistance because there is no diffusion potential in the MOSFET. Therefore, with the IGBT and the MOSFET connected in parallel to each other, it may be possible to reduce the loss of the semiconductor module. Moreover, it may be possible to further reduce the loss of the semiconductor module by increasing the chip area (or surface area) of the MOSFET.
However, the manufacturing cost of a wide-bandgap semiconductor is high. Therefore, increasing the chip area of the MOSFET, the manufacturing cost of the entire semiconductor module is accordingly increased. Moreover, in a high-current region, the bipolar effect of the IGBT becomes remarkable, lowering the on-resistance of the IGBT. Therefore, in the high-current region, the effect of connecting the MOSFET in parallel to the IGBT on reduction of the loss of the semiconductor module becomes small. Accordingly, in the high-current region, it is difficult to considerably reduce the loss of the semiconductor module by increasing the chip area of the MOSFET.